Atomic layer etching (ALE) is a plasma etch technology that enables layer-by-layer etching with atomic-scale precision. ALE implements a technique for removing thin layers of material using cycles of multi-steps that alternate, for example, between adsorption and desorption reactions. ALE is as an alternative to continuous etching and is viewed as an essential counterpart to atomic layer deposition.
Endpoint detection (EPD) is used to stop or change plasma etching processes by detecting that the material being etched has been cleared to an underlying layer. Depending on the types of materials being etched and the etch process parameters, a change of an optical emission spectrum of plasma at an endpoint of the etch process may be pronounced and relatively easy to detect, or conversely, subtle and relatively difficult to detect. For example, etching of the material with a low open ratio may make endpoint detection difficult using current algorithms for processing optical emission spectroscopy (OES) data. Improvements are therefore needed to make etch endpoint detection based on optical emission spectroscopy (OES) data more robust in such challenging etch process conditions.